This invention relates to an electrode-to-ballast interconnect of integral type compact fluorescent lamps with a discharge tube bent substantially in a plane, and, more particularly, a flat compact fluorescent lamp construction with built-in electronic ballast.
A flat compact fluorescent lamp construction of 2D type is disclosed in U.S. Pat. No. 4,458,301. This denomination of type originates from the shape of the glass discharge tube which resembles two upper case D letters standing in a mirror symmetry next to each other in a plane. When manufacturing these lamps, a straight tube, the inner portion of which is provided with phosphor coating, is used as a starting point. Stems mounted with electrodes and embedding electrode-in-leads and having a flared portion are sealed in both ends of the straight tube which is filled with a noble gas and additive during the sealing process. Subsequently, the straight tube is bent to a 2D shape. Owing to this manufacturing process, the electrode-in-leads embedded in the ends of the discharge tube are badly arranged. The electrode-in-leads may take up any position in the course of manufacturing so that an automated assembly of the discharge tube with the wires and a ballast circuit located in a base housing is limited. The base housing is positioned in a zone the boundary of which is defined by the discharge tube bent in the plane, and the ballast circuit is disposed on a circuit board which is substantially parallel to this plane. Although the electrode-in-leads are badly arranged, they extend from the tube ends substantially parallel to the plane of the circuit board. The problem arises how to usher the electrode-in-leads to the ballast circuit terminals located on the circuit board.
One solution to this problem is described in U.S. Pat. No. 5,627,433. In this solution, the electrode-in-leads of a compact fluorescent lamp, which also extend from the discharge tube parallel to the circuit board, are electrically connected to the ballast circuit by means of a mechanical connector component anchored in the circuit board. The barrel-like mechanical connector components receive and clamp the electrode-in-leads bent perpendicularly to the plane of the circuit board. Although this electrode-to-ballast interconnect results in a reliable electrical and mechanical connection, it suffers from drawbacks. Due to the complex nature and the small size of the mechanical connector component, an unduly precise electrode-in-lead positioning and pre-forming are required. Simultaneously, a precondition of forming faultless and reliable connection is that the tools of the high-speed automatic assembly machine used for positioning and inserting the leads work precisely.
The base housing of the compact fluorescent lamp construction of 2D type, which is disclosed in U.S. Pat. No. 4,458,301, protrudes from the plane of the discharge tube significantly and reduces the flatness of the lamp. The lamp fixtures accommodating these type of lamps however require a lamp which is as flat as possible.
Thus there is a particular need for an interconnect between the electrode-in-leads and the ballast circuit of a 2D type compact fluorescent lamp the manufacturing of which may be easily automated, provides a reliable connection and allows the base housing of the lamp to merge in the space defined by the discharge tube as much as possible.
As an exemplary embodiment of the invention, an electrode-to-ballast interconnect is provided in combination with a fluorescent lamp including a discharge tube bent substantially in a plane. The discharge tube is shaped at least in part to define a substantial portion of the boundary of a zone in the plane. The part of the tube defining the boundary includes at least one straight portion. The discharge tube has a symmetry axis in the plane and sealed tube ends provided with electrodes, and the tube ends re-enter said zone. A base housing is laid within said zone and receives the tube ends. The base housing includes a ballast circuit which is located at least partly on a circuit board positioned substantially parallel to the plane. The electrode-to-ballast interconnect comprises electrode-in-leads which are connected to each electrode and embedded in the tube ends. Terminals are anchored in and protruding from the circuit board. The electrode-in-leads are pre-formed to a shape suitable for connecting to the terminals. Means is formed in the circuit board for urging the electrode-in-leads to the terminals during assembly. The electrode-in-leads and the terminals are joined electrically and mechanically. In an exemplary embodiment of another aspect of the invention, an integral type compact fluorescent lamp comprises a base housing which is a flat body disposed at least partly within the space defined by the discharge tube. The base housing protrudes at most half of the outer diameter of the discharge tube from the space. At least one support arm extends from the base housing and is attached to a straight portion of the discharge tube. The part of the discharge tube, which defines the boundary, includes three straight portions to form a substantially rectangular zone and the tube ends re-enter the rectangular zone at the fourth side.
This construction has a number of advantages. One advantage over the prior art represented by U.S. Pat. No. 5,627,433 is that the electrode-to-ballast interconnect according to the present invention has a relatively simple and consequently a robust structure. This robust construction permits the manufacturing process of the interconnect to be easily automated and provides a reliable joint between the electrode-in-leads and the terminals of the ballast circuit. The electrode-in-leads of the compact fluorescent lamp described by U.S. Pat. No. 5,627,433 are less badly arranged than the electrode-in-leads of a 2D type lamp since they are embedded in pinch seals after bending the discharge tube. The pinch seals orientate the electrode-in-leads at a certain extent. Another advantage of the present invention with respect to U.S. Pat. No. 4,458,301 is that, even in the event of badly arranged electrode-in-leads, the structure of the electrode-to-ballast interconnect ensures a possibility of easy automation and a reliable electrical joint owing to the pre-forming of the electrode-in-leads and the means for urging the electrode-in-leads to the ballast terminals during assembly. These means are formed in the circuit board located substantially parallel to the plane in which the discharge tube is bent which, in turn, allows the base housing to be formed as flat as possible and to merge in the space defined by the discharge tube as much as possible. This is a basic advantage of the provided integral type compact fluorescent lamp, i.e. a lamp construction with built-in ballast circuit.